Hydroxyapatite Formation during Hydrothermal Liquefaction of Algae: Synthesis and Catalytic Implications

摘要/ Abstract标题：了解磷酸钙在污水藻类向生物原油热化学转化过程中改善油性质中的作用藻类作为可再生、经济实惠和低碳足迹燃料的潜在原料一直被研究。水热液化（HTL）是将湿藻转化为富碳生物原油的过程。HTL处理城市污水中生长的藻类已被证明可以生产具有与常规石油原油相似性质的生物原油。此外，废水喂养藻类的HTL导致固体生物炭产品的生产，迄今为止一直被认为是废物产品。然而，有证据表明，废水衍生的生物炭含有一种形式的磷酸钙，它可以作为催化剂，改善生物原油的组成和稳定性。堪萨斯大学的Susan Stagg-Williams教授和Belinda Sturm教授因了解生长条件、HTL反应中生物炭的形成、磷酸钙晶体的形成以及对生物原油产量和性能的最终影响之间的基本关系而获奖。这些知识对于可再生燃料和化学品的藻类技术的最终商业化是必要的。调查人员计划了各种教育项目，以提高公众对可持续能源生产的认识和参与。水热液化是一种很有前途的全细胞转化技术，利用亚临界水将藻类生物质转化为富含碳的生物原油。堪萨斯大学的初步工作已经证明，废水培养藻类的HTL导致高生物原油产量，低生物原油的O/C比，生物原油中高沸点化合物的水平较低，以及高生物炭的产量。表征研究表明，所产生的生物炭是一种钙缺乏取代羟基磷灰石（HAp）形式的磷酸钙。羟基磷灰石具有酸碱性质，对脱水和脱氢反应具有催化活性。在本研究中，将研究藻类和模型化合物的液化，以确定：1)藻类生长条件（Ca， N， P）对HTL反应器中HAp结晶的影响及其对生物原油组成的影响，2)HAp结晶形成对液化反应中形成的大分子单体的影响，以及3)液化过程中合成的HAp通过脱水和脱氢反应催化改变生物原油组成的能力。耦合控制HAp晶体生长与生物原油生产是一种新方法。了解生长条件、HAp的形成以及对生物原油产量和性能的最终影响之间的关系，对藻类HTL技术的最终商业化具有重要意义。这个项目的另一个支持获奖建议的方面是对环境的关注。增加关于应用藻类处理系统去除和回收城市和农业废水中的磷的基本知识应该产生积极的环境和经济影响。利用藻类处理系统作为一种低成本的营养物去除替代方案，同时产生生物原油和高价值的催化剂和生物材料，有可能将传统的监管操作（废水处理）转变为创收操作。

Abstract Title: Understanding the role of calcium phosphate in improving oil properties during thermochemical conversion of wastewater-fed algae to biocrude Algae have long been investigated as a potential feedstock for renewable, affordable, and reduced carbon-footprint fuels. Hydrothermal liquefaction (HTL) is a process to convert wet algae to a carbon-rich biocrude. HTL processing of algae grown in municipal wastewater has been shown to produce a biocrude with properties similar to conventional petroleum crude. Furthermore, the HTL of wastewater-fed algae results in the production of a solid biochar product, which has hitherto been considered a waste product. However, evidence shows that wastewater-derived biochar contains a form of calcium phosphate, which may act as a catalyst to improve biocrude composition and stability. An award is made to Professors Susan Stagg-Williams and Belinda Sturm of the University of Kansas to understand the fundamental relationships between growth conditions, the formation of biochar during the HTL reaction, the formation of calcium phosphate crystals, and the ultimate impact on biocrude yield and properties. This knowledge is necessary for the ultimate commercialization of algal technology for renewable fuels and chemicals. Various educational programs are planned by the investigators which will increase public awareness and engagement with sustainable energy production. Hydrothermal liquefaction has emerged as a promising whole cell conversion technology utilizing subcritical water to convert algal biomass to a carbon-rich biocrude. Preliminary work at the University of Kansas has demonstrated that HTL of wastewater-cultivated algae leads to high biocrude yields, low biocrude O/C ratios, low levels of high boiling point compounds in the biocrude, and high production of biochar. Characterization studies have shown that the biochar produced is a calcium-deficient substituted hydroxyapatite (HAp) form of calcium phosphate. HAp has been shown to have acid-base properties and be catalytically active for the dehydration and dehydrogenation reactions. In this study, the liquefaction of algae and model compounds will be investigated to determine: 1) the impact of algal growth conditions (Ca, N, P) on the crystallization of HAp in the HTL reactor and the resultant impact on biocrude composition, 2) the impact of the HAp crystallite formation on the macromolecule monomers formed during the liquefaction reaction, and 3) the ability of HAp synthesized during liquefaction to catalytically alter the biocrude composition through dehydration and dehydrogenation reactions. Coupling controlled HAp crystal growth with the production of biocrude is novel. Generating an understanding of the relationship between growth conditions, the formation of HAp, and the ultimate impact on biocrude yield and properties has significant merit for the ultimate commercialization of algal HTL technology. Another aspect of this project supporting the recommendation for award is the environmental focus. Increasing the fundamental knowledge about the application of algal treatment systems for phosphorus removal and recovery from municipal and agricultural wastewater should yield positive environmental and economic impacts. Utilizing algal treatment systems as a low-cost alternative to nutrient removal, while generating biocrude and high-value catalysts and biomaterials, has the potential to turn a historically regulatory operation (wastewater treatment) into a revenue-generating operation.